1. Field of the Invention
This invention relates to a mechanical pencil, and in particular to an automatic mechanical pencil, in which a chuck for gripping a lead is formed with plural chuck elements mutually combined with each other.
2. Description of the Related Art
In a mechanical pencil, when writing is effected, the chuck will grip the lead and the tip of the chuck is so formed that it can be opened and closed to release the gripping of the lead when the same is extended or sent out. In a commonly used chuck, the tip of the cylindrical chuck body is divided by slits into two or three gripping pieces, each of them is outwardly bent, and the tips are urged in the direction of opening. And, in case of writing, by means of a tightening ring put on the outer periphery of the chuck, the gripping pieces are tightened, and when the lead is extended or sent out, the tightening ring is shifted to release the tightening, and by the elastic restorable force of the bent gripping pieces, these pieces are expanded to open the tip of the chuck.
As mentioned above, usual chucks are so formed that the gripping pieces are expanded by the elastic action of metallic material; however, in case a chuck of similar construction normally made of metallic material is formed with plastic material, the forming is difficult and cannot be simply manufactured. It was proposed that plural chuck elements be provided and these be complementarily combined to form a chuck; however, to open the tip of the chuck under the combined state, there are many chucks formed by bending their tip of chuck elements outwardly.
On the other hand, in a pencil of a type which automatically sends out the lead, the chuck should be formed so as to release the gripping of the lead when the lead is sent out forwardly and to grip the lead when the lead is pushed backwardly. The chuck for assuring such a function is complicated in formation and cannot be manufactured economically.